System and method for increasing the temperature of gases within an exhaust of an internal combustion engine

ABSTRACT

Reformate gas is supplied into the exhaust  4  of an internal combustion engine  2  at a location upstream of an oxidation catalyst  6  and an ignition source  14  is provided either upstream or downstream of the oxidation catalyst and upstream of further exhaust gas treatment devices  8  for igniting the mixture in the exhaust to provide rapid heat up of the oxidation catalyst  6  and further exhaust gas treatment devices  8 . In a further embodiment reformate gas is injected into the exhaust  24  upstream of a turbocharger  26  to increase turbocharger boost pressure at low engine speeds.

TECHNICAL FIELD

The present invention relates to a system and method for increasing thetemperature of gases within an exhaust of an internal combustion engine,in particular in a diesel or lean-burn gasoline engine.

BACKGROUND OF THE INVENTION

Shortly after starting an internal combustion engine exhaust gastemperatures are low, especially at idle or low engine speeds.Accordingly it can take a considerable time period for componentsprovided within the exhaust, such as exhaust gas treatment devices andturbochargers, to reach a temperature required for correct operation.This is a particular problem in diesel engines since exhaust gastemperatures in diesel engines are generally relatively low compared tothose of equivalent petrol or gasoline engines. As such, it can take aconsiderable period of time after a cold engine start for exhaust gastreatment components, such as oxidation catalysts, particulate filtersand NOx traps, to reach the required operating temperature necessary forsatisfactory operation. Particulate filters in particular have to beregenerated from time to time. This requires a sufficiently hightemperature to burn off the soot trapped in the filter otherwise thefilter may become blocked and will subsequently break down resulting inhigh soot emissions from the exhaust.

Systems are known for providing additional combustion components andadditional air into an exhaust which are ignited in the exhaust in orderto increase the exhaust gas temperature and promote rapid heating ofexhaust gas treatment components and other components provided withinthe exhaust system.

Examples of such known systems are disclosed in GB2280128, EP0422432,DE19942711 and DE4142315. In each of the known systems, additional fuelis fed into the exhaust via the engine and additional air is injectedinto the exhaust downstream of the engine. In some cases an ignitionsystem, in the form of a spark plug or glow plug, is provided within theexhaust for igniting the fuel/air mixture contained therein.

Such known systems are unsatisfactory since the fuel supplied is thatused by the internal combustion engine and the excess fuel has to passthrough the combustion chamber before being ignited in the exhaust.Accordingly such systems can adversely affect the engine operatingconditions and cannot operate independently of the internal combustionengine. Furthermore, the burning of fuel and air within the exhaust cancause further emission problems unless accurate control of the air fuelratio within the exhaust system is maintained.

An object of the present invention is to provide a method and system forincreasing the temperature of the exhaust gases within the exhaust whichoperates independently of the engine operating conditions and avoids therisk of increased emissions of pollutants from the exhaust. Anotherobject of the present invention is to achieve rapid heating of theexhaust components during initial engine start up without damaging heatsensitive components, such as oxidation catalysts.

According to the present invention there is provided a method ofincreasing the temperature of exhaust gases within the exhaust of aninternal combustion engine comprising supplying a combustible gas intothe exhaust at a location downstream of a combustion chamber of theinternal combustion engine.

Preferably the method comprises the further steps of providing anignition source within the exhaust for igniting said combustible gas andoperating said ignition source to ignite said combustible gas in saidexhaust.

According to a further aspect of the invention there is provided asystem for increasing the temperature of exhaust gas within an exhaustof an internal combustion engine, said system comprising a source ofcombustible gas and means for injecting said combustible gas into theexhaust at a location downstream of a combustion chamber of the internalcombustion engine.

Preferably the system further comprises an ignition source for ignitingthe combustible gas within the exhaust.

In a preferred embodiment the combustible gas comprises reformate gas.Reformate gas comprises gaseous fuel having a high hydrogen content andcan be produced by reforming gasoline at high temperature (600° C. to900° C.) in the presence of a catalyst. Typically reformate gas has acomposition of 21% H₂, 23% CO, 0.5% CO₂, 1.5% CH₄ and 54% N₂.

In a preferred embodiment said combustible gas is supplied into theexhaust at a location upstream of a first exhaust gas treatment deviceprovided in the exhaust whilst said ignition source is provided at alocation either upstream or downstream of said first exhaust gastreatment device. Preferably said first exhaust gas treatment devicecomprises an oxidation catalyst.

Preferably further exhaust gas treatment devices, such as a particulatefilter and a NOx trap, are provided in the exhaust downstream of saidignition source such that the combustion of the combustible gas withinthe exhaust provides rapid heating of said further exhaust gas treatmentdevices such that said devices rapidly reach a required operatingtemperature.

In an alternative embodiment, a turbocharger is provided in the exhaustand the combustible gas is supplied into the exhaust at a locationupstream of the turbocharger. Combustion of the combustible gas upstreamof the turbocharger increases the temperature and volume of the exhaustgases and provides additional energy to the turbocharger providingincreased boost pressure and thus increasing the air mass within thecombustion chamber of the internal combustion engine improving enginetorque at low engine speeds, particularly at low load and/or low enginespeed.

An ignition source, such as a spark plug, may be provided in the exhaustupstream of the turbocharger, if required to ignite the combustible gas.

Preferred features and advantages of the invention will be apparent fromthe claims and from the following description.

SUMMARY OF THE INVENTION BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the invention will now be described, by way of exampleonly, with reference to the drawings, in which:

FIG. 1 is a schematic view of an internal combustion engine having asystem for increasing the temperature of gases within an exhaust systemaccording to a first embodiment of the present invention; and

FIG. 2 is a schematic view of a turbocharged internal combustion enginehaving a system for increasing the temperature of gases within anexhaust system according to a second embodiment of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

As shown in FIG. 1, an internal combustion engine 2 has an exhaustsystem 4 into which exhaust gases from the combustion chamber of theengine are passed. Within the exhaust system is a first exhaust gastreatment device 6, in the form of an oxidation catalyst, commonly knownas a catalytic converter, and secondary exhaust gases treatment devices8, such as a particulate filter and a NOx trap.

A source of combustible gas 10, in the form of hydrogen rich reformategas having a typical composition of 21% H₂, 23% CO, 0.5% CO₂, 1.5% CH₄and 54% N₂, is connected to the exhaust and means are provided forinjecting the combustible gas into the exhaust 4 at a location 12downstream of the internal combustion engine 2 and upstream of theoxidation catalyst 6. Unlike prior art systems, additional air is notsupplied into the exhaust. The system is primarily intended for use withlean burn engines where extra oxygen will normally be available withinthe exhaust gases.

The source of reformate gas can comprise an onboard reformer capable ofreforming hydrocarbon fuel, such as gasoline or diesel, into reformatehaving a high hydrogen content. Such onboard reformers are known andthus will not be described in more detail. Alternatively, oradditionally, the source of reformate gas may comprise a pressurisedcontainer containing a supply of reformate gas, possibly in addition toan onboard reformer for use during warm up of the onboard reformer.

Because the exhaust gas temperature may be insufficient forauto-ignition of the reformate gas and oxygen mixture, an ignitionsource, in the form of a spark plug 14, is provided in the exhaust 4.The spark plug 14 can be located either upstream or downstream of theoxidation catalyst 6 and upstream of the secondary exhaust gas treatmentdevices 8. If the spark plug 14 is located downstream of the oxidationcatalyst the reformate gas and oxygen mixture is ignited downstream ofthe oxidation catalyst 6, thus avoiding overheating of the oxidationcatalyst 6 which would occur when igniting the mixture upstream of theoxidation catalyst 6. This also enables a high initial rate of reformategas to be used to rapidly heat the exhaust gas treatment componentswithout the risk of damaging the oxidation catalyst. However, it may bemore desirable to locate the spark plug 14 upstream of the oxidationcatalyst 6 to provide rapid heating of the oxidation catalyst 6following engine start up.

A control device 16 is connected to the spark plug 14 to activate thespark plug 14 and ignite the reformate gas, when required. The controldevice 16 is preferably linked to the control of the supply of reformategas to the exhaust and, in the preferred embodiment, operates asfollows.

At engine start up reformate gas is supplied into the exhaust 2. If theexhaust gas temperature is below the light-off temperature of theexhaust components 6, 8, the spark plug 14 is activated to ignite themixture. Once the light-off temperature of the exhaust components 6,8has been reached the spark plug 14 might be deactivated.

The reformate gas injection will follow a programmed sequence. Initiallythe reformate gas will be supplied at a high rate to achieve a fastsystem heat up. Once the target temperature for the exhaust components6, 8 has been reached the reformate gas supply rate is reduced to alower rate sufficient to compensate for heat losses in the exhaust. Asdescribed above, by initially igniting the reformate gas downstream ofthe oxidation catalyst 6, a high initial supply rate of reformate gascan be used to increase the speed of system heat up without riskingdamage to the oxidation catalyst 6.

Whilst an ignition source in the form of a spark plug 14 is specificallydisclosed it is envisaged that a glow plug might be used as analternative, simplifying the ignition source control device 16.

By supplying the reformate gas to the exhaust 4 upstream of theoxidation catalyst 6, the CO and HC components of the reformate gas canbe oxidized by the oxidation catalyst 6 to provide acceptable emissionlevels even where a high rate of reformate gas is supplied for prolongedperiods.

The embodiment of the present invention shown in FIG. 1 and describedabove is particularly suitable for diesel engines, wherein the exhaustgas temperature is relatively low compared to that of a gasoline engineand thus the time taken for exhaust gas treatment devices, in particularoxidation catalysts, to reach their required operating temperature canbe excessive, leading to emission problems in the period following acold start of the engine. Furthermore, diesel engines are normallyfitted with particulate filters to prevent the emission of soot from theexhaust. If the exhaust gas temperature is insufficient to enableregeneration of the particulate filter to take place, the particulatefilter can become clogged leading to break down of the filter and highsoot emissions from the exhaust. The present invention avoids suchproblems by ensuring the particulate filter rapidly reaches thetemperature required for regeneration and ensuring such temperature ismaintained during operation of the engine.

FIG. 2 shows a second embodiment of the present invention.

An internal combustion engine 22, which may be either gasoline or dieselfuelled, has an exhaust 24 in which is situated a turbocharger 26whereby the energy of the exhaust gases from the engine 22 is used todrive a turbine operatively linked to a compressor supplied with airfrom an air inlet duct 28 and supplying compressed air to air outletduct 30 connected to the intake manifold of the internal combustionengine 22 increasing the pressure of the air supplied to the intake ofthe internal combustion engine. One or more exhaust gas treatmentdevices 32 are provided downstream of the turbocharger 22.

Turbochargers can provide increased torque by increasing the chargedensity within the combustion chamber of the internal combustion engine.However, at low load and/or low speed engine conditions there may beinsufficient energy in the exhaust gases to drive the turbochargerresulting in low boost pressure and low engine torque under suchconditions.

In order to overcome this problem a source of combustible gas 34,preferably in the form of hydrogen rich reformate gas having a typicalcomposition of 21% H₂, 23% CO, 0.5% CO₂, 1.5% CH₄ and 54% N₂, isconnected to the exhaust and means are provided for injecting thecombustible gas into the exhaust 24 at a location 36 downstream of theinternal combustion engine 22 and upstream of the turbocharger 26.

By introducing a combustible gas into the exhaust 24 at a location 36upstream of the turbocharger 26 combustion occurs within the exhaust,increasing the temperature and volume of the exhaust gas, increasing thespeed of the turbine of the turbocharger and providing additional boostpressure, thus increasing engine torque, particularly at low enginespeed.

As with the first embodiment, the combustion of reformate gas within theexhaust also rapidly heats the exhaust gas treatment components 32within the exhaust to the required operating temperature necessary forsatisfactory operation and maintains said exhaust gas treatmentcomponents, such as an oxidation catalyst, at the required operatingtemperature.

If required, an ignition source, such as a spark plug or glow plug, maybe provided within the exhaust for igniting the mixture of reformate gasand oxygen contained therein.

Whilst in the preferred embodiment the combustible gas comprisesreformate gas, it is envisaged that other combustible gases or othercombustible products may be used. FIG. 1 is a schematic view of aninternal combustion engine having a system for increasing thetemperature of gases within an exhaust system according to a firstembodiment of the present invention; and

FIG. 2 is a schematic view of a turbocharged internal combustion enginehaving a system for increasing the temperature of gases within anexhaust system according to a second embodiment of the presentinvention.

As shown in FIG. 1, an internal combustion engine 2 has an exhaustsystem 4 into which exhaust gases from the combustion chamber of theengine are passed. Within the exhaust system is a first exhaust gastreatment device 6, in the form of an oxidation catalyst, commonly knownas a catalytic converter, and secondary exhaust gases treatment devices8, such as a particulate filter and a NOx trap.

A source of combustible gas 10, in the form of hydrogen rich reformategas having a typical composition of 21% H₂, 23% CO, 0.5% CO₂, 1.5% CH₄and 54% N₂, is connected to the exhaust and means are provided forinjecting the combustible gas into the exhaust 4 at a location 12downstream of the internal combustion engine 2 and upstream of theoxidation catalyst 6. Unlike prior art systems, additional air is notsupplied into the exhaust. The system is primarily intended for use withlean burn engines where extra oxygen will normally be available withinthe exhaust gases.

The source of reformate gas can comprise an onboard reformer capable ofreforming hydrocarbon fuel, such as gasoline or diesel, into reformatehaving a high hydrogen content. Such onboard reformers are known andthus will not be described in more detail. Alternatively, oradditionally, the source of reformate gas may comprise a pressurisedcontainer containing a supply of reformate gas, possibly in addition toan onboard reformer for use during warm up of the onboard reformer.

Because the exhaust gas temperature may be insufficient forauto-ignition of the reformate gas and oxygen mixture, an ignitionsource, in the form of a spark plug 14, is provided in the exhaust 4.The spark plug 14 can be located either upstream or downstream of theoxidation catalyst 6 and upstream of the secondary exhaust gas treatmentdevices 8. If the spark plug 14 is located downstream of the oxidationcatalyst the reformate gas and oxygen mixture is ignited downstream ofthe oxidation catalyst 6, thus avoiding overheating of the oxidationcatalyst 6 which would occur when igniting the mixture upstream of theoxidation catalyst 6. This also enables a high initial rate of reformategas to be used to rapidly heat the exhaust gas treatment componentswithout the risk of damaging the oxidation catalyst. However, it may bemore desirable to locate the spark plug 14 upstream of the oxidationcatalyst 6 to provide rapid heating of the oxidation catalyst 6following engine start up.

A control device 16 is connected to the spark plug 14 to activate thespark plug 14 and ignite the reformate gas, when required. The controldevice 16 is preferably linked to the control of the supply of reformategas to the exhaust and, in the preferred embodiment, operates asfollows.

At engine start up reformate gas is supplied into the exhaust 2. If theexhaust gas temperature is below the light-off temperature of theexhaust components 6, 8, the spark plug 14 is activated to ignite themixture. Once the light-off temperature of the exhaust components 6,8has been reached the spark plug 14 might be deactivated.

The reformate gas injection will follow a programmed sequence. Initiallythe reformate gas will be supplied at a high rate to achieve a fastsystem heat up. Once the target temperature for the exhaust components6, 8 has been reached the reformate gas supply rate is reduced to alower rate sufficient to compensate for heat losses in the exhaust. Asdescribed above, by initially igniting the reformate gas downstream ofthe oxidation catalyst 6, a high initial supply rate of reformate gascan be used to increase the speed of system heat up without riskingdamage to the oxidation catalyst 6.

Whilst an ignition source in the form of a spark plug 14 is specificallydisclosed it is envisaged that a glow plug might be used as analternative, simplifying the ignition source control device 16.

By supplying the reformate gas to the exhaust 4 upstream of theoxidation catalyst 6, the CO and HC components of the reformate gas canbe oxidized by the oxidation catalyst 6 to provide acceptable emissionlevels even where a high rate of reformate gas is supplied for prolongedperiods.

The embodiment of the present invention shown in FIG. 1 and describedabove is particularly suitable for diesel engines, wherein the exhaustgas temperature is relatively low compared to that of a gasoline engineand thus the time taken for exhaust gas treatment devices, in particularoxidation catalysts, to reach their required operating temperature canbe excessive, leading to emission problems in the period following acold start of the engine. Furthermore, diesel engines are normallyfitted with particulate filters to prevent the emission of soot from theexhaust. If the exhaust gas temperature is insufficient to enableregeneration of the particulate filter to take place, the particulatefilter can become clogged leading to break down of the filter and highsoot emissions from the exhaust. The present invention avoids suchproblems by ensuring the particulate filter rapidly reaches thetemperature required for regeneration and ensuring such temperature ismaintained during operation of the engine.

FIG. 2 shows a second embodiment of the present invention.

An internal combustion engine 22, which may be either gasoline or dieselfuelled, has an exhaust 24 in which is situated a turbocharger 26whereby the energy of the exhaust gases from the engine 22 is used todrive a turbine operatively linked to a compressor supplied with airfrom an air inlet duct 28 and supplying compressed air to air outletduct 30 connected to the intake manifold of the internal combustionengine 22 increasing the pressure of the air supplied to the intake ofthe internal combustion engine. One or more exhaust gas treatmentdevices 32 are provided downstream of the turbocharger 22.

Turbochargers can provide increased torque by increasing the chargedensity within the combustion chamber of the internal combustion engine.However, at low load and/or low speed engine conditions there may beinsufficient energy in the exhaust gases to drive the turbochargerresulting in low boost pressure and low engine torque under suchconditions.

In order to overcome this problem a source of combustible gas 34,preferably in the form of hydrogen rich reformate gas having a typicalcomposition of 21% H₂, 23% CO, 0.5% CO₂, 1.5% CH₄ and 54% N₂, isconnected to the exhaust and means are provided for injecting thecombustible gas into the exhaust 24 at a location 36 downstream of theinternal combustion engine 22 and upstream of the turbocharger 26.

By introducing a combustible gas into the exhaust 24 at a location 36upstream of the turbocharger 26 combustion occurs within the exhaust,increasing the temperature and volume of the exhaust gas, increasing thespeed of the turbine of the turbocharger and providing additional boostpressure, thus increasing engine torque, particularly at low enginespeed.

As with the first embodiment, the combustion of reformate gas within theexhaust also rapidly heats the exhaust gas treatment components 32within the exhaust to the required operating temperature necessary forsatisfactory operation and maintains said exhaust gas treatmentcomponents, such as an oxidation catalyst, at the required operatingtemperature.

If required, an ignition source, such as a spark plug or glow plug, maybe provided within the exhaust for igniting the mixture of reformate gasand oxygen contained therein.

Whilst in the preferred embodiment the combustible gas comprisesreformate gas, it is envisaged that other combustible gases or othercombustible products may be used.

1. A method of increasing the temperature of exhaust gases within theexhaust of an internal combustion engine comprising supplying acombustible gas into the exhaust at a location downstream of acombustion chamber of the internal combustion engine.
 2. A method asclaimed in claim 1, comprising the further steps of providing anignition source within the exhaust for igniting said combustible gas andoperating said ignition source to ignite said combustible gas in saidexhaust.
 3. A method as claimed in claim 1, wherein the combustible gascomprises reformate gas.
 4. A method as claimed in claim 2, wherein thecombustible gas comprises reformate gas.
 5. A system for increasing thetemperature of exhaust gas within an exhaust (4, 24) of an internalcombustion engine (2, 22), said system comprising a source (10, 34) ofcombustible gas and means for injecting said combustible gas into theexhaust (4, 24) at a location downstream of a combustion chamber of theinternal combustion engine.
 6. A system as claimed in claim 5, furthercomprising an ignition source (14) for igniting the combustible gaswithin the exhaust (4).
 7. A system as claimed in claim 5, wherein thecombustible gas comprises reformate gas.
 8. A system as claimed in claim6, wherein the combustible gas comprises reformate gas.
 9. A system asclaimed in claim 6 when dependent upon claim 5, wherein said combustiblegas is supplied into the exhaust (4) at a location (12) upstream of afirst exhaust gas treatment device (6) provided in the exhaust (4)whilst said ignition source (14) is provided at a location eitherupstream or downstream of said first exhaust gas treatment device (6).10. A system as claimed in claim 7 when dependent upon claim 5, whereinsaid combustible gas is supplied into the exhaust (4) at a location (12)upstream of a first exhaust gas treatment device (6) provided in theexhaust (4) whilst said ignition source (14) is provided at a locationeither upstream or downstream of said first exhaust gas treatment device(6).
 11. A system as claimed in claim 9, wherein said first exhaust gastreatment device (6) comprises an oxidation catalyst.
 12. A system asclaimed in claim 9, wherein further exhaust gas treatment devices (8),such as a particulate filter and a NOx trap, are provided in the exhaust(4) downstream of said ignition source (14).
 13. A system as claimed inclaim 11, wherein further exhaust gas treatment devices (8), such as aparticulate filter and a NOx trap, are provided in the exhaust (4)downstream of said ignition source (14).
 14. A system as claimed inclaim 5, wherein a turbocharger (26) is provided in the exhaust (24) andthe combustible gas is supplied into the exhaust (24) at a location (36)upstream of the turbocharger (26).
 15. A system as claimed in claim 6,wherein a turbocharger (26) is provided in the exhaust (24) and theignition source is located upstream of the turbocharger (26).
 16. Asystem as claimed in claim 15, wherein the ignition source is a sparkplug.
 17. A system as claimed in claim 7, wherein a turbocharger (26) isprovided in the exhaust (24) and the combustible gas is supplied intothe exhaust (24) at a location (36) upstream of the turbocharger (26).